1. Field of the Invention
The present invention relates to projection tube apparatuses, and more specifically, to projection tube apparatuses equipped with deflection devices for deflecting an electron beam emitted from an electron gun in vertical and horizontal directions.
2. Description of the Related Art
Generally, for higher resolution of projection-type projection televisions, a deflection field of a deflection device equipped with its projection tube apparatus is a substantially uniform magnetic field. Thus, pincushion distortions 1 (1a, 1b) of an image that occur due to geometric reasons as shown in FIG. 11 remain, and a correction circuit of a projection television set correct these pincushion distortions 1. Particularly, it is known that the proportion of the power necessary to correct the pincushion distortion 1a in upper and lower portions of the screen accounts for at least 10% of the entire power consumption of a projection television set. With an increasing demand for energy saving in recent years, projection television set manufacturers are facing design difficulties.
Conventionally, in order to solve the above-described problems, techniques as given below have been proposed (see e.g., JP 2003-123669A).
FIG. 12 shows a side view of a conventional deflection device. As shown in FIG. 12, the conventional deflection device 2 is made up of horizontal deflection coils 3, vertical deflection coils 4, and a core 5. In the vicinity 6 of an opening on the screen face side of the deflection device 2, horizontal correction coils 7 and vertical correction coils 8 are disposed at the left and right and the top and bottom of the opening, respectively. Here, the horizontal correction coils 7 are connected to the horizontal deflection coils 3 in series, and the vertical correction coils 8 are connected to the vertical deflection coils 4 in series.
The operation of the conventional deflection device 2 configured as above, particularly the operation of the vertical correction coils 8 is described below with reference to FIG. 13. FIG. 13 is a diagram for schematically describing the operation of the conventional deflection device. As shown in FIGS. 12 and 13, when a vertical deflection current passes through the vertical deflection coils 4, a current passes through the vertical correction coils 8 disposed at the top and bottom in the vicinity 6 of the opening on the screen face side of the deflection device 2, thereby generating a correction field 9. Thus, an electron beam 10 is subjected to the Lorentz force 11 in the direction away from the Z axis (the tube axis) in the vicinity of the upper and lower portions of the screen, and the pincushion distortion in the upper and lower portions of the screen is corrected. Similarly, when a horizontal deflection current passes through the horizontal deflection coils 3 and when a current passes through the horizontal correction coils 7, pincushion distortion in the left and right portions of the screen is corrected.
However, in the technique disclosed in JP 2003-123669A, the horizontal correction coils 7 and the vertical correction coils 8 are necessary in addition to the deflection device 2, and the number of manufacturing steps required for assembling these coils also increases, resulting in a problem of an increase in cost of the deflection device 2.
The present invention has been made in order to solve the above-described problem in the conventional art, and it is an object of the present invention to provide a projection tube apparatus that can correct the pincushion distortion at the upper and lower portions of the screen without adding any other components such as correction coils.